I honestly do not understand how the entire game is related to the cartridge since this game is about nuclear bomb, a glowing man, and who is cassie?
Old cartridge is just a physical representation of a lost game and it’s still a mystery why the developer threw it away and it is not yet clear what he’s hiding or trying to say. Some people that had near death experiences sometimes witness unusual supernatural things, so the “glowing guy” is just a messenger of incoming inevitable doom. Also Cassie is/was a daughter of the involved character, but the whole family was out of town and are still missing.